The Urban Stormwater Management Manual for Malaysia or the Manual Saliran Mesra Alam Malaysia (MSMA) is the urban drainage design procedure first published by the Department of Irrigation and Drainage Malaysia in early 2000. It is mandatory for all engineers in Malaysia to build drainage works to comply with the requirements of MSMA. The Department of Irrigation and Drainage has completely amended the first edition of MSMA (known as MSMA1) with the publication of the second edition (known as MSMA2) about Eleven years after its first edition. There are a lot of alterations in the second edition including the following (based on case studies completed for Kuala Lumpur):
For Kuala Lumpur it was found that the design storm has increased by up to 126% for 10 out of the fourteen rainfall stations.
The design flow using the Rational Method has increased by up to 131% for commercial and city area.
The Site Storage Requirement for On-Site Detention for a factory lot in Kuala Lumpur has increased by up to 235%,
Detention pond has risen by up to 130% in the volume.
The changes between the first and the second editions of MSMA give rise to the increase in the values of the main design parameters below:
135 stations in Peninsular Malaysia with longer precipitation record. The rainfall intensities for most ARI’s have increased.
Compared to the first edition where it was divided into east and west coast of the Peninsula for the derivation of the storm temporal pattern, West Malaysia is now separated into 5 regions. The dissimilar hydrograph peaks and shapes caused by the changes in temporal patterns.
Not dependent on storm durations and intensities, and whether a catchment is urban/rural in condition, the coefficient of runoff in the Rational Method is now set according to the types of landuse. Changes in the estimated peak flow is observed .
The changes in the storm intensites, temporal patterns and the loss model used all influenced the Time-Area Method in MSMA2. For Kuala Lumpur it is noted that the storm intensities have increased and the storm temporal pattern is more peaky, thus giving rise to a more peaky flow hydrograph.
The Site Storage Requirement (SSR) based on the Approximate Swinburne Method in the second editon is higher than that using the Swinburne Method in MSMA1. The approximate method in the second editon has caused an over estimation of the SSR’s.
Compared to the first edition, the increase in the storm intensities, temporal patterns and the selection of loss rate have resulted a rise in the storage of a detention basin using the second edition.
A software tool Is built to assist engineers to carry out the computations using both editions precisely and to allow comparison be made of their differences quickly, due to the many changes in computational methods between the first and second editions of MSMA. A stormwater design software is designed for MSMA. The software is developed by Ir. Dr. Quek Keng Hong- a practising engineer in Malaysia. MSMAware also covers the East Malaysian state of Sarawak where more than a dozen rainfall stations and their temporal patterns are programmed into the software.